Lateral Stability

[Tonic Please]

Hi. Im off to Canada tommorow to finish off some things. I need to nkow the answer to a question I am confused about.

The book goes on about Pendulous stabily, and all other kinds. One question is "what is the name for stabilty in pitch roll and yaw"...Well, he talks about 5 other types and I dont know which three to choose.

The main prob I have also is "name three methods to achieve lateral stabilty"

Please help! Dont be too complicate :confused:

Smooth skies,

Dan.

[Tinstaafl]

Tonic, I'm having trouble working exactly what it is you know/don't know/want to know.

Could you elaborate please?

NB. I think you're asking for 3 ways to increase lateral stability. You've already mentioned one way in your post (Pendulous Stability: gained by having high set wings).

Other ways include:

Dihedral: Wing tips are higher than the wing root. Easily seen from behind or in front of the a/c.

High set keel area: An example is the fin giving a large area above the Centre of Gravity.

Swept wings: Wing tips are aft of the wing root. Easily seen on just about every jet a/c. Look up as one flies over the top of you! NB: Lateral stability is not the main purpose of swept wings on these a/c however it is a side effect.

[No. 2]

Tonic,

Is this what you were after?

1. Pitch: Longitudinal stability
2. Roll: Lateral Stability
3. Yaw: Directional Stability

No. 2

[Genghis the Engineer]

(Just talking about static stability here, dynamic stability is much more complicated)

Longitudinal stability = pitch stability = speed stability = stick force (or displacement) per airspeed change. Affected by tailplane size, longitudinal dihedral (which is the difference in incidence between the mainplane and stabiliser), washout (in a swept wing), control system gearing.

[Close relative, manoeuvre stability which is (pull) stick-force per g.]

Directional stability = weathercock effect = yawing moment due to sideslip Achieved by sweep, or by having more side area behind the CG than in front of it - area a long way behind the CG is more useful than just behind - hence the fact we put the tail at the back.

Lateral stability = dihedral effect = pendular stability = rolling moment due to sideslip. Achieved by sweep, dihedral, having the CG below the wing.

And don't let anybody convince you that you need lots of any of these, you need the right amount of all of them. Too much longstab and the pitch control forces are too high, too much lat-stab and the aircraft rolls too much in turbulence, too much directional stab and it yaws too much in turbulence, also you will struggle to kick off drift in a crosswind landing.

Hope this helps,

G

[No. 2]

Tonic,

To add to the above post, longitudinal static stability is dependent on the position of the CG relative to the aerodynamic centre. For positive stability this will be aft of the CG.

[Tonic Please]

Great! I can see how he "hid" the explination in the text now. Complicated stuff!

Thanks agian...and Tinnstaafl...You answered the question so no need to elaborate :)

Smooth skies,

Dan... (canda in3 hours!) :D